I have dis-assembled my hydraulic motor before when I was trouble shooting an issue. Turned out it wasn't the motor, but one of the 50 amp breakers that was checking good with an ohm meter, but wasn't actually working. The point being, the motor was full of carbon dust from the brushes and I think really benefited from the thorough cleaning. Perhaps that is your issue?
2016 F350 CC Dually Powerstroke 4x4
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